1. Field of the Invention
Embodiments disclosed herein generally relate to blowout preventers used in the oil and gas industry. Specifically, embodiments selected relate to blowout preventers with a novel seal assembly to seal between high-pressure and low-pressure zones.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, safety devices must be put in place to prevent injury to personnel and damage to equipment resulting from unexpected events associated with the drilling activities.
Drilling wells involves penetrating a variety of subsurface geologic structures, or “layers.” Occasionally, a wellbore will penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with a kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high-pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high-pressure region to a low-pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. Such “blowouts” may result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and substantial injury or death of rig personnel.
Because of the risk of blowouts, devices known as blowout preventers (“BOPs”) are installed above the wellhead at the surface or on the sea floor in deep water drilling arrangements to effectively seal a wellbore until active measures can be taken to control the kick. BOPs may be activated so that kicks are adequately controlled and “circulated out” of the system. There are several types of BOPs, the most common of which are annular blowout preventers and ram-type blowout preventers. From this point further, ram-type blowout preventers will be discussed in more detail.
Referring to FIG. 1, an example of a ram-type BOP 100 is shown. Ram-type BOP 100 typically includes a body 102 and at least two oppositely disposed bonnets 104. Bonnets 104 may be secured to body 102 with, for example, bolts and/or a hinge so that bonnet 104 may be removed for maintenance. Alternatively, as shown in FIG. 1, bonnets 104 may be secured to body 102 using radial lock mechanism 106 to enable bonnets 104 to slide and rotate when necessary for maintenance.
Engaged within each bonnet 104 is a piston actuated ram 108. Typically, rams 108 are either pipe or variable bore rams which, when activated, move to engage and surround drillpipe and/or well tools to seal the wellbore, shear rams which, when activated, move to engage and physically shear any drillpipe and/or well tools in the wellbore, or blind rams which, when activated, move to engage and close the wellbore when no drillpipe is present. Rams 108 may be located opposite of each other along an axis 112 and may seal against one another proximate a center of a wellbore 110. More discussion of ram-type blowout preventers and high-pressure seals is provided in U.S. Pat. No. 6,554,247 (“the '247 patent”), issued to Berckenhoff, assigned to the assignee of the present invention, and incorporated herein by reference in its entirety.
As with any tool used in drilling oil and gas wells, blowout preventers must be sealed and secured to prevent potential hazard to the surrounding environment and personnel. For example, ram-type BOPs may include high-pressure seals between the bonnets and the body of the BOP to prevent leakage of fluids. In many instances, the high-pressure seals are elastomeric seals and should be checked regularly to ensure that the elastomeric components have not been cut, permanently deformed, or deteriorated by, for example, a chemical reaction with the drilling fluid in the wellbore.
Referring now to FIG. 2 (taken from the '247 patent), an example of a ram-type BOP 200 includes a high-pressure face seal carrier 202 to seal between a bonnet 104 and a body 102. Face seal carrier 202 is disposed in a groove 204 formed in bonnet 104 about axis 112. Face seal carrier 202 includes two elastomeric o-ring seals 206, 208 and a biasing mechanism 210. O-ring seals 206, 208 sealingly engage surfaces of body 102 and bonnet 104, while biasing mechanism 210 biases face seal carrier 202 from bonnet 104 towards body 102. One concern with a seal of this type is that in a BOP, the bonnet and the body of the BOP may need to be larger to accommodate a face seal. For example, face seal carrier 202 is retained within a face surface 212 of bonnet 104 to seal against body 102. This requires bonnet 104 (and corresponding body 102) to be radially larger to retain face seal assembly 104 than may be necessary for a radial seal. Furthermore, face seals may be more susceptible to a loss of seal integrity. For example, when sealing across imperfections and defects (e.g., scratches, gouges, abrasions) in seal surfaces, face seals may be more susceptible to have leak across the seal.
Referring now to FIG. 3A, an example of a radial seal 302 is shown schematically. FIG. 3A is taken from U.S. Pat. No. 3,887,198 (issued to McClure et al. and incorporated herein by reference in its entirety). As shown, radial seal 302 is disposed in a groove 306 of a shaft 304 and seals between shaft 304 and body 308. A fluid F enters through a clearance 310 between shaft 304 and body 308 into groove 306. Fluid F enters under high pressure and thrusts radial seal 302 to sealingly engage with another clearance 312 between shaft 304 and body 308. Similarly, in another schematic example shown in FIG. 3B, a radial seal 302 may further include a ring 314 to ensure proper spacing of radial seal 302 between body 308 and shaft 304. FIG. 3B is taken from U.S. Pat. No. 3,970,321 (issued to Dechavanne and incorporated herein by reference in its entirety). A concern with these types of sealing assemblies, though, may relate to the inability to seal at low pressures. For example, under low pressure, radial seal 302 may not have enough fluid F to pressurize and thrust radial seal 302 into sealing engagement with clearance 312.
Referring now to FIG. 4, another example of a ram-type BOP 400 including a radial seal 408 is shown. Radial seal 408 is disposed in a groove 406 formed in a bonnet 404 about axis 112. Retainer 407 is used to retain radial seal 408 within groove 406. Radial seal 408 seals between bonnet 404 and a body 402. As shown, radial seal 408 includes multiple rings 410 that may provide structural support for radial seal 408. A concern with radial seals is that under high pressure, body 402 may expand about axis 112, while bonnet 404 remains relatively dimensionally stable. In such a condition, radial seal 408 may not be able to effectively seal between body 402 and bonnet 404.
Accordingly, there exists a need for a sealing assembly to seal between surfaces under high pressure without sacrificing sealing capabilities under low pressure.